The invention relates, in general, to an optical system that includes a convergent lens for injecting laser radiation emitted from a semiconductor laser into an optical device, and to a method for producing a plurality of plano-convex convergent lenses which can be used in such an optical system.
In optical information transmission, radiation from semiconductor laser emitters, which generally emit widely divergent beams, has to be injected into optical conductors, such as optical fibers. Furthermore, the power to be injected has to be matched to the requirements of various transmissions systems and standards.
In known laser modules involving information transmission technology (see, for example, DE 41 33 220), the laser emitter is followed by a spherical, biconvex or plano-convex lens that converts the highly divergent beam into a convergent beam. In order to inject the desired radiation power into the optical conductor, the optical conductor must be adjusted in all three spatial directions. These systems thus involve a very high level of assembly effort, in particular because of the complex adjustment in the z-direction. Furthermore, mechanical instabilities often occur in these systems.
A further disadvantage of the known optical systems of the type mentioned initially is that additional technical means have to be used to prevent the laser radiation that is not injected into the optical conductor from emerging from the corresponding component. European Patent Application EP 0 566 341 A1, which represents the closest prior art, describes a connector device for connecting a laser diode to an optical fiber. The connector device comprises a plano-convex lens configured in the beam path on the light inlet side, a diaphragm plate configured behind the lens, and an optical connecting element provided on the light outlet side. The lens, diaphragm plate, and optical connecting element are located (for reasons of mutual alignment) in a common socket, and their touching surfaces are bonded using a transparent adhesive.
It is accordingly an object of the invention to provide an optical system that includes a convergent lens for injecting laser radiation emitted from a semiconductor laser into an optical device and a method for producing the convergent lens which overcome the hereinafore-mentioned disadvantages of the heretofore-known methods and devices of this general type in such a way that the optical device can be easily adjusted.
In particular, it is an object to provide an optical system by means of which the radiation power to be injected into the optical device (optical conductor) can be varied in a simple manner.
In particular, the convergent lens is provided with a structured coating in the form of a diaphragm (for example a perforated or zone diaphragm) for masking out a portion of the laser radiation emitted from the semiconductor laser emitter. This is achieved by configuring the convergent lens to pass only that portion of the laser beam emitted from the semiconductor laser emitter that is intended to be injected into the optical conductor.
Masking out the laser radiation with a high divergence angle advantageously improves the quality of the focusing of the convergent lens. A major advantage of the optical system according to the invention is, in particular, that the portion of the beam emitted from the semiconductor laser emitter which is in any case not injected into the optical conductor is masked out. In consequence, receptacle components advantageously achieve the same eye safety as pigtail components.
With the foregoing and other objects in view there is provided, in accordance with the invention, an optical system that includes a semiconductor laser for emitting laser radiation, an optical device, and a convergent lens. The convergent lens is configured between the semiconductor laser and the optical device for injecting the emitted laser radiation into the optical device. The convergent lens is provided with a coating structured to have the form of a diaphragm for masking out a portion of the emitted laser radiation.
In accordance with an added feature of the invention, there is provided a structured coating (diaphragm) which is preferably composed of metal, and which can be applied in a simple manner to the surface of the convergent lens, by means of vapor deposition. The convergent lens may be composed of glass, silicon or some other semiconductor material that passes the respective laser radiation wavelength. It is particularly preferred for the convergent lens to be a plano-convex lens, with the structured coating provided on the convex side.
In accordance with an additional feature of the invention, there is provided a structured coating that is preferably in the form of a perforated diaphragm and that masks out the portion of the laser radiation whose divergence angle is greater than the acceptance angle of the optical conductor. The radiation power injected into the optical conductor is varied by varying the divergence angle below the value of the acceptance angle, without having to change the geometrical configuration of the entire system that includes the semiconductor laser emitter, convergent lens, and optical device that can be an optical conductor.
In accordance with another feature of the invention, there is provided a structured coating that is preferably in the form of a zone diaphragm for masking out the high-intensity central beam. This reduces the injected power and increases the eye safety of receptacle versions.
In accordance with a further feature of the invention, the optical system may be employed in an advantageous manner for coupling the laser beam of the semiconductor laser emitter in a multi-mode fiber. Only the fundamental mode of the multi-mode fiber is stimulated by masking out the laser radiation with a high divergence angle. The transmission characteristics of a single mode fiber are thus simulated in the multi-mode fiber.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for producing a multiplicity of plano-convex focusing lenses. An Silicon wafer is first produced which is provided with a plurality of convex elevations on a first main surface, using photographic techniques and etching. A first metallic layer is applied which is by using photographic techniques and etching, structured such that, on the convex elevations, (ring-shaped) perforated diaphragms or disc-shaped zone diaphragms remain. Once its second main surface has been bonded onto an adhesive film, for example, the silicon wafer is then sliced through, for example, by sawing or cutting grinding, to form individual plano-convex convergent lenses with a perforated diaphragm or zone diaphragm.
The use of the optical system according to the invention is, of course, not limited for injecting laser radiation into an optical fiber. It can be used in any apparatus in which only a portion of an available laser beam is intended to be injected into an optical device.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an optical system for injecting laser radiation into an optical conductor, and a method for its production, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.